Ferguson, furious with referee Steve Bennett for signalling four minutes' injury time as United held on to a 1-0 lead, made the fist-pumping gesture when Cristiano Ronaldo scored the late second goal after a touchline run-in with Reading coach Wally Downes.

The FA confirmed they will study video evidence of the incident and ask Ferguson to explain his actions. He is just back from a touchline ban after being fined £5,000 for using 'foul and abusive language' at Bolton.

Ferguson, speaking in Riyadh ahead of United's testimonial game against Al Hilal tonight, said: "All I was doing was expressing my relief at winning what was one of our hardest matches of the season."